1. Field of the Invention
The present invention relates to a pin tumbler lock.
2. Description of the Prior Art
Tumbler locks have been configured essentially permitting absolutely no change in unlocking conditions. On the other hand, a variety of more or less flexible locks have been provided recently, which may be re-set to operate under different unlocking conditions to repel the original key used during a construction work. However, such a lock of the prior art has such drawbacks as alteration of the unlocking condition is confined to only once and moreover provides no free conditioning so that the existing lock must be replaced if the current key is lost or to prevent others from attempting a trespass. More flexible locks have been recently provided permitting multiple re-setting after manufacture. The U.S. Pat. No. 3,999,413 discloses for example a lock assembly of the wafer tumbler type.
On the other hand, although a lock assembly of the pin tumbler type is also provided to permit multiple re-setting, it has generally remained intricate in construction and no simple assembly is available as the wafer type. The U.S. patent application Ser. No. 393,493 filed on Aug. 28, 1964 for example relates to a lock assembly of the pin tumbler type, but the lock of this reference comprises an adjustment mechanism which changes the length of tumblers and is operable from outside by means of a special element for exclusive use, bearing a disadvantage of an intricate and large construction so that it may be inapplicable to a low cost, simple lock.